Thixotropic dispersions of polysuccinimide and their use

ABSTRACT

The present invention relates to stable thixotropic polysuccinimide (PSI) dispersions, known as slurries, and to their use as additives for improving the flow properties of concrete, in oil wells, in acidic gel cleaners, and in drainage systems of tunnel constructions.

BACKGROUND

[0001] The present invention relates to stable thixotropicpolysuccinimide (PSI) dispersions, known as slurries, and to their useas additives for improving the flow properties of concrete, in oilwells, in acidic gel cleaners, and in drainage systems of tunnelconstructions. Stable in the sense of the present invention means stableagainst separation of liquid and solid compounds.

[0002] Polyaspartic acids and their salts have in recent years attractedincreased interest as biodegradable alternatives to polyacrylic acids.

[0003] The preparation of polyaspartic acids by a variety of processeshas been investigated in depth. For example, the condensation ofaspartic acid or ammonium maleate and/or the dehydration productsthereof leads to the intermediate polysuccinimide (PSI), which byhydrolysis under alkaline conditions forms salts of polyaspartic acid.If polysuccinimide is exposed to water under initially neutralconditions, then slowly polyaspartic acid is formed, and a pH of 2.5-3is established. Under acidic conditions at room temperature, thehydrolysis comes to a standstill (Mosig, Gooding, Wheeler, Ind. Eng.Chem. Res. 1997, 36, 2163-2170).

[0004] In the course of the investigations on the hydrolysis of PSI aspart of the present invention, the influence of particle size and hencealso of the water/PSI phase boundary on the hydrolysis rate of PSIitself became clear. The investigations showed that the hydrolysis rateis directly proportional to the particle surface area. Reaction ofpolysuccinimide and water under increased pressure and elevatedtemperature produces a mixture of aspartic acid and its oligomers.

[0005] Because of their acidic properties, polyaspartic acids are highlyeffective in the breakup or reformation of deposits, such as those ofcalcium carbonate. The effect is founded firstly on the pH in theimmediate vicinity of the opening succinimides in the PSI, secondly,following neutralization of the polyaspartic acid, on the dispersingaction of the polyaspartate anion.

[0006] The use of polyaspartic acid in an acidic environment ishindered, however, by its instability under these conditions.Polyaspartic acid is subject to acidic hydrolysis to monomeric asparticacid, especially under a thermal load (investigations by Bayer AG,brochure “PASP Na-Salz”—polyaspartic acid sodium salt; a new,biodegradable dispersant, Edition 3.99, Order No.: CH 201201). It waspossible to show that a 1% strength polyaspartic acid undergoes 61%hydrolysis after 24 h at a pH of 4, 77% hydrolysis at a pH of 2, whichparticularly in the case of oil wells is disadvantageous.

[0007] Cleaners very often contain viscosity-increasing substances.Examples of cleaners are given in U.S. Pat. No. 6,083,890 with xanthanas thickener, in U.S. Pat. No. 6,004,916 with ammonium EDTA ascomplexing agent and a solvent, and also nonionic surfactants asdispersion media, and in U.S. Pat. No. 5,554,320 with phosphoric acidand paraffinsulfonate, fatty alcohol-EP/PO copolymer as surfactant.

[0008] With the direct use of polyaspartic acid in oil wells, a problemwhich is found is that the polyaspartic acid becomes diluted as a resultof diffusion following its introduction into the bore hole. As a result,the concentration may fall below optimum ranges.

[0009] JP-A 8 169 741 describes the use of powderous polysuccinimide forimproving the flow behavior of mortar mixtures with Portland cement.Incorporation in powder form, however, is typical, since uniformdistribution within the cement mortar is achieved only by prolongedmixing. Uniform distribution is absolutely necessary, sinceinhomogeneities lead to problems with the ultimate hardness of thecement. It would be advantageous to provide PSI as a paste or dispersionin water, in which the wetting of the polysuccinimide by water hadalready taken place and which would therefore prevent the lumping thatoccurs in the course of stirred incorporation.

[0010] The object was therefore to find thixotropic formulations of PSIwith water which meet all of these requirements as regards stability andliquefiability.

[0011] Stable in the sense of the present invention has been alreadydiscussed above but also refers to the feature that the thixotropicdispersions of the invention maintain their useful form or usefulchemical/physical nature for a reasonable storage period.

[0012] Surprisingly, thixotropic dispersions of PSI with water accordingto the present invention exhibit all of these properties.

SUMMARY

[0013] The invention relates to a stable thixotropic dispersioncomprising polysuccinimide in a protic solvent.

[0014] The invention also relates to a process for preparing athixotropic polysuccinimide dispersion comprising: (a) introducingpolysuccinimide and/or its copolymers to a vessel, (b) adding a proticsolvent and surfactant to the vessel and mixing, thereby forming amixture, (c) thoroughly mixing the mixture, thereby forming ahomogeneous dispersion, and (d) solidifying the homogeneous dispersion.

[0015] These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

DESCRIPTION

[0016] The present invention accordingly provides thixotropicdispersions of polysuccinimide and protic solvents, preferably withwater, with particular preference deionized water, which furthercomprise a hydrocolloid, preferably a surfactant, with particularpreference an anionic or nonionic surfactant.

[0017] PSI in the fine-particled state required for the thixotropicdispersions of the invention may be prepared in accordance with theprocesses of DE-A 19 706 901 or EP-A 0 786 487, incorporated herein byreference in their entirety.

[0018] The thixotropic PSI dispersions of the invention contain fromabout 10 to about 90% by weight of PSI, preferably from about 30 toabout 70% by weight of PSI, with particular preference from about 40 toabout 60% by weight of PSI.

[0019] The thixotropic PSI dispersions of the invention are prepared byintensively stirring a finely particulate polysuccinimide having atypical particle size in the maximum of a few hundred μm. Ideally, a PSIhaving a particle diameter of from about 10 to about 250 μm, preferablyfrom about 10 to about 150 μm, with particular preference from about 10to about 100 μm, and, with very particular preference, of from about 10to about 70 μm in the maximum of the distribution is used. The largesurface area is advantageous for the rapid establishment of equilibrium.

[0020] The thixotropic PSI dispersions of the invention contain fromabout 0.01 to about 20% by weight of surfactants, preferably from about1 to about 10% by weight of surfactants, with particular preference fromabout 1 to about 5% by weight of surfactants.

[0021] The function of the surfactant is to disperse the PSI as finelyas possible. In this context, both nonionic and anionic surfactants aresuitable in principle; owing to the positive charge, cationicsurfactants may lead to instances of flocculation of electroneutralaggregates with the polyaspartate anion.

[0022] Preferred surfactants in the context of the present invention arenonionic surfactants, with particular preference fatty alcoholethoxylates, with very particular preference C₁₄-C₁₆ fatty alcoholshaving a degree of ethoxylation of 20-40.

[0023] Besides surfactants the thixotropic PSI dispersions of theinvention may comprise thickeners, with particular preferencebiodegradable thickeners.

[0024] In one preferred embodiment, biodegradable thickeners are addedto the thixotropic PSI dispersions. In the context of the presentinvention, preferred thickeners used are cellulose ethers. In thecontext of the present invention, a particularly preferred thickenerused is methylcellulose.

[0025] The PSI dispersions of the invention are obtainable by dispersingthe PSI in a protic solvent, preferably water, especially deionizedwater. The dispersions of the invention are prepared by firstintroducing PSI and/or its copolymers, adding the water and homogenizingthe water thoroughly using an Ultra-turrax—or a similar stirringapparatus suitable for the present purpose. Thereafter, the surfactantis added and thorough mixing with the Ultra-turrax is repeated. Finally,a homogeneous dispersion is obtained which soon solidifies after thestirring operation.

[0026] PSI represents an alternative to polyaspartic acid because it canbe converted into a fine, stable dispersion which does not sediment andwhich, through an increase in viscosity, substantially suppressesdiffusion and thus hydrolysis in water.

[0027] Furthermore, by means of the PSI dispersions of the invention itis possible to achieve a higher storage stability of polyaspartic acid.In application, an inventive PSI dispersion is able to be liquefied bymeans of shear forces, so making available polyaspartic acid in themanner of a sustained release effect. The amount of polyaspartic acidpresent in equilibrium with polysuccinimide under these conditions isavailable in order, for example, to break up calcium carbonateencrustations. The polyaspartic acid then removed from the system byneutralization can be reformed by hydrolysis, so that there is alwayssufficient (although low) concentrations of free polyaspartic acidavailable.

[0028] Fine stable PSI dispersions of the invention, known asthixotropic PSI dispersions, are also suitable for use as acidic gelcleaners, such as, for instance, in the sanitary segment for dissolvinglime deposits. Ideally, a gel cleaner flows along the surface to becleaned, but thickens when there are no shear forces and so remainsadhering to the surface. The contact time, especially in the case ofvertical surfaces, remains greatly increased, as does, consequently, thecleaning effect when thixotropic PSI dispersions according to thepresent invention are used.

[0029] In the use in oil wells it is advantageous to have thethixotropic PSI dispersion which solidifies after being pumped in oilwells and which releases polyaspartic acid only gradually.

[0030] In tunnel drainage systems it is possible under certaincircumstances for instances of sintering to occur, leading to blockageof the piping system. Often, these sites are inaccessible. There again,it is advantageous to have the thixotropic PSI dispersion according tothe present invention which solidifies at the blockage points afterbeing pumped into the piping system and which releases active substance(polyaspartic acid) at the site over a prolonged period, and which leadsto concentration gradients with local maxima.

[0031] The thixotropic PSI dispersions of the invention exhibit thedesired viscosity behavior, the stability needed for the above-mentionedapplications, and also liquefiability. Generally the dispersions arestable at least 300 days at a temperature that is less than about 20°C., or from at least 200 days at a temperature that is less than about25° C., or from at least 150 days to about 200 days at a temperatureranging from about 25° C. to about 30° C.

[0032] They are therefore suitable for use in cement or concrete forimproving its flow properties, in drainage systems of tunnelconstructions, in oil wells, and in acidic gel cleaners.

[0033] In acidic gel cleaners, the thixotropic PSI dispersions of thepresent invention permit the cleaning of sanitary installations or ofscratch-sensitive surfaces such as, for example, plastics, bronze,brass, silver, lead crystal or glass ceramic hobs.

[0034] The present invention therefore also relates to cements orconcretes and also gel cleaners which comprise a flow-property-improvingfraction of thixotropic PSI dispersions.

[0035] The invention is further described in the following illustrativeexamples in which all parts and percentages are by weight unlessotherwise indicated.

EXAMPLES Example 1

[0036] Approximately 50:50% by weight PSI/water slurries were admixedwith 3-5% by weight fatty alcohol ethoxylates and intensively stirredwith the Turrax stirrer. After leaving them to stand for 24 hours, theirviscosity as a function of the shear rate was measured using arotational viscometer. A curve typical of that for thixotropic liquidswas found.

[0037] FIGS. 1 and 2 show by way of example two measurements of a PSIslurry of 47.5% by weight PSI, 47.5% by weight water and 5% by weightDisponil®. Disponil® is a surfactant from Henkel AG

[0038] FIGS. 3 and 4 show by way of example two measurements of a PSIslurry of 48.5% by weight PSI, 48.5% by weight water and 3% by weightDehydol®. Dehydol® is a surfactant of Henkel AG.

Example 2

[0039] Water-based PSI slurries may be prepared using a thickener evenwith relatively small amounts of active substance, as the followingexample shows.

[0040] 10 g of polysuccinimide were dispersed in 250 ml of water. Thedispersion sediments over the course of 15 minutes. A correspondingmixture was admixed with 15 g of methylcellulose and stirred intensivelyfor 30 minutes. The gelatinous dispersion formed remains stable for 14days.

Example 3

[0041] A formulation according to Example 1 was capable of dissolvingcalcium carbonate, as the following example shows:

[0042] In a reaction vessel, 200 ml of the slurry from Example 1 wereadmixed under nitrogen atmosphere with 10 g of finely powderedlimestone, and the mixture was stirred intensively. A stream of nitrogenwas passed through the vessel, and was subsequently passed through abarium hydroxide solution (Barytes water). Over the course of 5 minutes,a marked clouding of the barium hydroxide solution was observed as aresult of the carbon dioxide liberated from the limestone. The controltest without polysuccinimide shows no clouding of the barium hydroxidesolution.

Example 4

[0043] Two limestone blocks originating from a tunnel were placed eitherin 200 ml of a slurry of 60% by weight H₂O and 40% by weight PSI and 2%by weight surfactant or in 200 ml of mains water and were stirred with amagnetic rod arranged to the side of them. In no case was any evolutionof gas observed.

[0044] After one week at room temperature the blocks were removed, freedfrom adhering slurry with distilled H₂O, and dried to constant weight:Block in PSI slurry Block in mains water (PSI content: 60%) (17° dH*)Initial weight: 42.4945 g Initial weight: 40.363 g Final weight: 37.5483g Final weight: 40.359 g Difference: 4.9462 g = 11.6% Difference: 0.004g =0%

[0045] The test clearly shows the breakup of a limestone block by 11.6%after just one week, initiated by the use of a slurry of the invention.

Example 5

[0046] In a shaft of a tunnel drainage system with greatly reduced waterflow (water: pH 8 23° dH), the following PASP concentrations wereobtained following the application of 500 g of polysuccinimide or 1000 gof PSI dispersion: as tabs(2.5 cm diameter, compressed about 3 ppm with10% stearic acid) as dispersion (48.5% PSI>30 ppm 3% Dehydol®) measured1 week following application of the PSI application form.

[0047] Although the present invention has been described in detail withreference to certain preferred versions thereof, other variations arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the versions contained therein.

What is claimed is:
 1. A stable thixotropic dispersion comprisingpolysuccinimide in a protic solvent.
 2. The dispersions according toclaim 1, wherein the dispersion comprises a hydrocolloid.
 3. Thedispersion according to claim 2, wherein the dispersion furthercomprises an anionic or nonionic surfactant.
 4. The dispersion accordingto claim 1, wherein the protic solvent is water.
 5. The dispersionaccording to claim 2, wherein the surfactant is a fatty alcoholethoxylate.
 6. The dispersion according to claim 1, wherein thedispersion contains from about 10 to about 90% by weight ofpolysuccinimide and from about 0.01 to about 20% by weight of asurfactant.
 7. The dispersion according to claim 1, wherein thedispersion further comprises biodegradable thickeners.
 8. A process forpreparing a thixotropic polysuccinimide dispersion comprising: (a)introducing polysuccinimide and/or its copolymers to a vessel, (b)adding a protic solvent and surfactant to the vessel and mixing, therebyforming a mixture, (c) thoroughly mixing the mixture, thereby forming ahomogeneous dispersion, and (d) solidifying the homogeneous dispersion.9. A cement composition or a concrete composition comprising aflow-property-improving fraction of a thixotropic polysuccinimidedispersion.
 10. An acidic gel cleaner composition comprising aflow-property-improving fraction of a thixotropic polysuccinimidedispersion.